1. Field of the Invention
The present invention relates to a method for printing a digital document by a cut sheet printing system on a plurality of cut sheets, resulting in an end product having a reader spread formed by two opposing sheets of the plurality of sheets, each cut sheet of the plurality of sheets having a first side and a second side, the first side having a first print characteristic and the second side having a second print characteristic different from the first print characteristic. As is well known, a reader spread comprises at least a part of each of two neighboring sides and each of the neighboring sides is a side of a different sheet of the plurality of sheets.
The present invention further relates to a cut sheet printing system configured to perform the method according to the present invention.
2. Description of Background Art
Printing systems for digital cut sheet printing are nowadays also used for printing books and other documents having both sides of the sheets printed upon with images. Such a printing system may comprise a tandem construction of two print engines or two print heads, each print engine or print head printing on one predetermined side of the cut sheets. The cut sheets are separated from a media input holder with one predetermined side upwards. On the other hand, such a printing system may comprise a turning-over unit for turning over a cut sheet between a first printing action of printing on one side of the cut sheet and a second printing action of printing on the other side of the cut sheet. The first printing action and the second printing action may be done by a same print head or print engine or by different print heads or print engines. The cut sheets are printed in a cut sheet printing sequence order. If, for example a book is printed, the pages 1 and 2 may be printed on sides of a first cut sheet, the pages 3 and 4 may be printed on sides of a second cut sheet after printing of the pages 1 and 2, etc. If, for example a booklet or a signature is printed comprising an even number n of pages, the pages 1 and n may be printed on a first side of a cut sheet, the pages 2 and n−1 may be printed on a second side of the same cut sheet, and the cut sheet may be folded in half later on after printing on the cut sheet has finished.
FIG. 4 illustrates an example of a print sequence of cut sheets for duplex printing and a corresponding reader spread in the end product according to the background art. FIG. 7 shows an example of a diagram of a background art method for duplex printing of cut sheets.
FIG. 4 illustrates a print sequence PS of sides of cut sheets numbered 1 and 2 for duplex printing on both sides of the cut sheets 1, 2. The cut sheet numbered 1 has a front side indicated by the text “1: front” and a back side indicated by the text “1: back” and provided with the number “2.” The cut sheet numbered 2 has a front side indicated by the text “2: front” and a back side indicated by the text “2: back.” The plurality of images to be printed in an end product on subsequent pages on both sides of the cut sheets 1 and 2 are the images provided with large numbers “1”, “2”, “3” and “4.” The print order of the plurality of images will now be explained in combination with a flow diagram of a method according to the background art as shown in FIG. 7. A starting point A leads to a first step S1.
According to the first step S1 the cut sheet numbered 1 is separated from the input holder of a cut sheet printing system and transported to the print engine.
According to a second step S2, a bitmap representing the large number “1” is printed upon the front side of the cut sheet numbered 1.
According to a third step S3, the cut sheet numbered 1 is transported to a known duplex print loop module and is turned by the duplex print loop module.
According to a fourth step S4, the cut sheet numbered 1 is transported again to the print engine and a bitmap representing the large number “2” is printed upon the back side of the cut sheet numbered 1.
According to a fifth step S5, the cut sheet numbered 1 is deposited in an output holder of the cut sheet printing system.
According to the sixth step S6, the cut sheet numbered 2 is separated from the input holder of the cut sheet printing system and transported to the print engine.
According to a seventh step S7, a bitmap representing the large number “3” is printed upon the front side of the cut sheet numbered 2.
According to an eighth step S8, the cut sheet numbered 2 is transported to the duplex print loop module again and is turned by the duplex print loop module.
According to a ninth step S9, the cut sheet numbered 2 is transported again to the print engine and a bitmap representing the large number “4” is printed upon the back side of the cut sheet numbered 2.
According to a tenth step S10, the cut sheet numbered 2 is deposited in the output holder of the cut sheet printing system. The method ends in an end point B.
The steps S1-S5 may be executed in parallel or interleaved with the steps S6-S10.
The resulting reader spread RS (See FIG. 4) shows that the two subsequent pages having the prints of the bitmaps representing the numbers “2” and “3” form a reader spread. The first page of this reader spread with the number “2” is printed on the back side of the cut sheet numbered 1, while the second page of this reader spread with the number “3” is printed on the front side of the cut sheet numbered 2. The reader spread is printed on sides of different print characteristics.
After printing of all the cut sheets, the printed cut sheets may be gathered into a printed document. The printed document comprises two-page spreads in which the left part of the spread is printed on the first side of a cut sheet, while the right part of the spread is printed on the second side of another cut sheet. A reader spread may usually be printed on cut sheets, which are subsequent in the cut sheet printing sequence order.
Since the first side of a cut sheet has a different print characteristic than the second side of a cut sheet, a print quality consistency difference, like a color consistency difference, may appear in the printed document, especially in a reader spread.